The polyphenylene ethers are known and described in numerous publications including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875 and Stamatoff U.S. Pat. Nos. 3,257,357 and 3,257,358. The high-molecular weight polyphenylene ethers are high performance engineering thermoplastics possessing relatively high-melt viscosities and softening points--i.e., in excess of 275.degree. C., and are useful for many commercial applications requiring high-temperature resistance including formation of films, fibers and molded articles.
Although they have the above-described desirable properties, it is also known that certain properties of the polyphenylene ether resins are undesirable for some commercial uses. For example, parts molded from the polyphenylene ethers are somewhat brittle due to poor impact strength. In addition, the relatively high-melt viscosities and softening points are considered a disadvantage for many uses. Films and fibers can be formed from polyphenylene ether resins on a commercial scale using solution techniques, but melt processing is commercially unattractive because of the high temperatures required to soften the resin and the problems associated therewith such as instability, discoloration and the requirement for specially designed process equipment to operate at elevated temperatures. Molded articles can be formed by melt processing techniques, but, again, the high temperatures required are undesirable.
It is known in the art that properties of the polyphenylene ether resins can be materially altered by blending them with other resins. For example, one method for improving the melt processability of the polyphenylene ethers is disclosed in a commonly-assigned patent, U.S. Pat. No. 3,379,792, incorporated herein by reference. According to this patent, flow properties of the polyphenylene ethers are improved by blending with from about 0.1 to 25 parts by weight of a polyamide. In another commonly-assigned patent, U.S. Pat. No. 3,361,851, a polyphenylene ether composition comprising a polyphenylene ether blended with a polyolefin is disclosed. The polyolefin is added to improve impact strength and resistance to aggressive solvents. In a third commonly-assigned patent, Cizek, U.S. Pat. No. 3,383,435, there are provided means for simultaneously improving the melt processability of the polyphenylene ether resins while simultaneously up-grading many properties of polystyrene homopolymer and random copolymer resins. The invention of the Cizek patent is based upon the discovery tha the polyphenylene ether resins and such polystyrene resins, including rubber modified polystyrene resins, are combinable in all proportions and result in compositions having many properties improved over those of either of the components.
One preferred embodiment of the Cizek patent is a composition comprising a high-impact, rubber reinforced polystyrene and a poly(2,6-dialkyl-1,4-phenylene) ether. This composition was preferred because it provides the aforementioned objectives of improving the melt-processability properties of the polyphenylene ether resin and provides the further advantage of improving impact resistance of parts molded from the blend. Furthermore, the Cizek composition of the polyphenylene ether and the high-impact polystyrene could be custom-formulated to provide predetermined properties ranging between those of the polystyrene and those of the polyphenylene ether by controlling the ratio of the two polymers. The reason for this is that the blend exhibits a single set of thermodynamic properties rather than two distinct sets of properties--i.e., one for each of the components of the blend as is typical with blends of prior art.
The styrene resins disclosed in the Cizek patent are either homopolymers or random copolymers. For example, the crystal polystyrenes of Examples 1 and 9 are homopolymers. Lustrex HT-88 of Example 7 is a commercial styrene grafted butadiene rubber modified high-impact polystyrene. In such products a portion of the styrene is homopolymerized into side chains onto a rubber backbone. The styrene containing copolymer resins disclosed in Cizek, Column 2, are random copolymers: styrene acrylonitrile, styrene-butadiene, styrene-acrylonitrile-.alpha.-alkyl styrene copolymers, styrene-acrylonitrile-butadiene (ABS), copolymers of ethylvinyl benzene and divinyl benzene and the like. With the exception of styrene-acrylontirile-.alpha.-methyl styrene, Example 17, none of the Cizek terminology can be construed to disclose a block copolymer of the A-B-A type. Because the monomers are grafted into terminal blocks, instead of side chains, A-B-A block copolymers are more linear and their properties differ markedly from the grafted rubber copolymers used in Cizek.
It is known from U.S. Pat. No. 3,660,531 to Lauchlan et al, that A-B-A block-type polymers have been employed in combination with polyphenylene ether resin compositions. The particular type of A-B-A polymer disclosed by Lauchlan et al is of the type that was used in Example 3. That copolymer is based on a B block that was essentially a butadiene moiety. These copolymers are distinctly different from the A-B-A block copolymers employed in the present invention which have what may be called an essentially olefinic rubber midblock and not a diene rubber midblock.
It has now been discovered that a hydrogenated block copolymer of the A-B-A type wherein A designates a polymerized mono-alkenyl aromatic hydrocarbon block such as polystyrene and B designates a polymeric diene block which has had its unsaturation reduced by hydrogenation to less than 10% of the original saturation, will impart unexpectedly high-impact strengths to polyphenylene ether resins and compositions of polyphenylene ether resins and polystyrene homopolymer and random copolymer resins. For example, a composition of 35 parts by weight of a polyphenylene ether resin, 50 parts by weight of a rubber-modified, high-impact polystyrene resin and 15 parts of a block copolymer of the A-B-A type wherein B is an olefin rubber midblock, had an Izod impact strength of 9.1 ft. lbs./in. notch. Also compositions according to this invention have high-heat deflection temperatures, high Gardner impact resistance, high thermal oxidative resistance, uv stability, high surface gloss and good resistance to solvents such as gasoline.